Piston



UCL 8, 1940 J. FLAMMANG ET A1. 2,217,541

PISTON Filed Sept. l5, 1957 2 Sheets-Sheet l Ff'y. R,

ATTORNEYS.

Patented Oct. 8, 1940 f UNITED STATES PATENT OFFICE I St. Louis, William M.

Venner, Richmond Heights, and Percy L. Bowser, Jr., University City, Mo., assignors to The Sterling Corporation, St. Louis, Mo., a corporation of Delaware Application September 15, 1937, Serial No. 163,888

4 Claims.

This invention pertains to trunk pistons such as are used in internal combustion engines and has particular application to pistons cast of light metal such as aluminum, magnesium or its alloys having a high rate of thermal expansion, although it may also be applied to other types of pistons.

It has been found that, although aluminum has a much greater rate of thermal expansion than cast iron of which engine cylinders are usually constructed, aluminum pistons can be .made without slotting or otherwise cutting the skirt to render it yieldable, which will operate with perfect satisfaction throughout thev working range of temperatures involved in the operation of the usual automobile engine.

One of the objects of this invention, therefore, is to provide a so-called solid skirt piston in which the flexibility of the skirt is so controlled and the skirt is so connected with the head that the play of forces between the head and skirt taking place upon rise of temperature and due to relative expansion of those parts will cause a de frmation of the bearing portions of the skirt in such a manner as to maintain a substantially constant bearing of the skirt upon the cylinder wall.

Another object is to provide a piston structure in which the paths provided for the flow of heat from the head to the skirt are so-arranged as to provide diierences of temperature Ain different portions of the head and skirt such that the expansion of the hotter portions will mechanically deflect cooler portions in such a manner as to maintain the t of the piston in the cylinder.

Another object is to provide a structure whereby the relative transverse and longitudinal flexibility of the skirt may be adapted to the forcesof expansion involved in the operation thereof.

Further objects will appear from the following description taken in connection with the accompanying drawings in which- Figure 1 is a side view ofk a piston embodying this invention.

Figure 2 is a section on line 2-2 of Figure 1.

Figure 3 is a bottom view of the piston shown in Figure 1.

Figure 4 is a section on line 4- 4 of Figure 1. Figure 5 is a longitudinal section through the wrist pin axis of a piston similar to that of Figure 1 but havingV in addition a stiiening web along the thrust face.

, Figure 6 is a section on line B-B'of Figure 5.

Figure '1 is a view similar to Figure 5 showing two ribs instead of one.

55 Figure 8 is a section on line 8-8 of Figure 7.

Wrist pin bosses 4.

Figure 9 is a view similar to Figure 5, but showing three ribs, and

Figure 10 is a section on line Ill-lll of Figure 9( Referring to the drawings, I designatesl the head of the piston and 2 indicates the skirt gen- 5 erally. Extending downwardly from the head are connectors 3 which carry at their lower ends the The connectors 3 may be stiffened and braced against the head by one or more internal ribs 5. 10 Extending horizontally at the lower ends of the connectors 3 are beams indicated generally at 6. These extend in a chordal direction with reference to the skirt rand transversely of the wrist pin axis. `These beams, in the embodiment il- 15 lustrated in the drawings, are placed substantially at the extreme lower ends of the wrist pin bosses and are reinforced or stiffenedby one or more webs I extendingy horizontally along the beams Ii.k In the embodiment illustrated in the 20 drawings three such webs are shown so as to render the cross beams very stil and rigid. It will be seen that the structure including the head, the. connectors and bosses with their bracingk ribs 5 and the transverse beams 6 with their stifiening 25 webs 1 provide a very rigid frame structure for supporting the skirt.

.skirt terminates in a circumierentially continuous rim. 9 which is separated from the bosses 4, and the beams 6 by horizontally extending perforations IIJ.` These rim portions are thus not only 35 rendered more exible but the separation cuts qu direct iiow of heat from the pin bosses to this rim and, by forcing a longer path of ow for the heat,- keeps this portion of the skirt cooler.

The upper ends of the thrust bearing portions 40 8 are separated from the head I by horizontal slots Il. These portions are further separated from the adjacent portions of the connectors 3 by downwardly extending recesses I2. By this structure the upper end of each thrust bearing '45 portion 3 is made to project upwardly from the beams 6 in cantilever relationthereto so that this portion, being freed from the rigid support of the beams, is enabled to flex more readily than i the lower portions of these thrust faces. The V provision of the recesses I2 also tends to lengthen the path of heat ow from the head to the upper ends of the thrust bearing portions 8 just below the slots Il. These upper ends are thereby kept cooler so that a' greater difference of temperature 55 will be maintained between these points and the head I.

In order to control the flexibility of the thrust bearing portions 8 these portions are made thinner at the upper ends thereof than at the lower ends. This may be done by gradually flaring the bore of this portion of the skirt upwardly as indicated in dotted lines in Figure 2.

While it is not desired to limit this invention to any particular theory of action, it is believed that the following action takes place and that the functioning of the piston will be explained thereby. When the piston operates in the engine under normal conditions, the heat of the combustion gases is applied to the head I and flows downwardly therefrom through the connectors 3 and the bosses 4 to the skirt and is transferred to the cylinder wall through those portions of the skirt which contact therewith. Accordingly, there is a continual transfer of heat from the head I to the cylinder wall and, as a result, there will be a continual fall of temperature from the head along the path of heat flow. Ordinarily the temperature will be lower in those portions which are further from the head measured along the path of heat flow. Accordingly, the bosses 4 and the beams 6 will ordinarily be at a higher temperature than the thrust bearing portions 8. Similarly, those bearing portions will ordinarily be at a higher temperature at their middle portions where they are joined to the beams 6 than at their upper and lower portions which are farther from the source of heat measured along the path of flow. The separated rim portions 9 will also be lower in temperature than the bearing portions 8. Since the structure, including the head, the connectors 3 and the beams 6, is at a higher temperature, this portion will have a r greater expansion than the skirt. Under this expansion the beams 6 will tend to separate along the wrist pin axis. As the ends of these beams are connected to the bearing portions 8 and the latter are lower in temperature, mechanical forces will be set up tending to stretch these bearing portions along the wrist pin axis. This stretching action will tend to draw inwardly the central portions of the bearing faces. Now, in order to take advantage of this action, the piston skirt is originally machined so as to have a slightly elliptical eccentricity with the major axis of the ellipse extending transversely of the wrist pin axis, and the minor axis of the ellipse extending along the wrist pin axis. With a skirt so shaped and the degree of eccentricity properly adjusted the stretching action may be made to compensate almost exactly for the tendency of the bearing faces to expand under heat and the bearing diameter of the thrust faces can thereby be maintained substantially constant.

Since the upper ends of the bearing portions 8 are separated only a slight distance from the head I, some transfer of heat may take place by radiation across the slots II. However, by virtue of the recesses I2 the path of heat flow to this portion of the skirt is increased in length so that the temperature of the upper end o! each bearing portion 8 may be kept the same or lower than that of the intermediate part of those bearing portions.V Accordingly, the fit of the upper ends of the portions 8 may be controlled along with that of intermediate portions by the stretching action mentioned above.

It will be noted further that the beams 6 are constructed so as to be rigid so that their deiiection under the above-mentioned stretching action will be small. Accordingly, the i'ull effect of the expansion of the head is delivered to the thrust portions 8. The effect of the recesses I 2 in addition to that mentioned above is to cause the overhang of the upper end of the thrust portions 8 beyond the support of the beams 6 so that said upper ends are rendered more flexible so that they may yield to the thrust pressure of the cylinder upon the piston wall.

The lower end of the skirt is probably the coolest portion thereof and it will be noted that by placing the beams 6 at the extreme lower end of the bosses said beams are placed close to the lower edge of the skirt and their stretching action is effective in causing the reduction in diameter along the major axis of the ellipse, and this is the more effective on account oi.' the probably greater difference in temperature between this portion of the skirt and the head. It has been found in practice that with this structure and a proper eccentricity of the elliptical form a substantially uniform fit of the skirt in the cylinder is maintained throughout the working range of temperature.

In certain pistons where the dimensions are such as to render the skirt portion flexible not only transversely but longitudinally, it may be desirable to reduce the exibility in the longitudinal direction. For this purpose internal stiffening ribs I3 may be provided extending longitudinally of the thrust bearing portions 8. One or more ribs may be used. In Figures 5 and 6 one rib is shown extending along the middle of the portion 8. In Figures 7 and 8 two ribs are provided near the outer edges of that portion, while in Figures 9 and 10 three ribs are provided. 'Ihe distribution of these ribs should be such as to reserve the transverse flexibility of the bearing portions while providing stiffness in a longitudinal direction of the proper degree. Instead of extending full length of the bearing section these ribs may be terminated short of the upper or lower ends of the skirt in order to control the flexibility in all directions of the bearing portions.

It is desirable to have the bearing portions 8 somewhat more flexible, longitudinally or transversely, or both, at their ends than .at an intermediate portion. The beams 6 -tend to stiifen the intermediate portion somewhat, so that this result is accomplished by an un-ribbed structure such as shown in Figure 2. With skirts of different dimensions such relative flexibility may be attained by the use of ribs I3 of proper length and positioning.

It is obvious that various changes in the details of construction within the scope of the appended claims may be made without departing from the spirit of this invention. Accordingly, it is understood that the invention is not limited to the specific details shown or described.

Having thus described the invention, what is claimed is:

1. A trunk piston of the character described, having a head, pin-boss connectors extending downwardly from said head, a skirt provided with a thrust-bearing portion separated from said head and extending between said connectors, said portion being more flexible transversely at its upper end than at its lower end and having means for stiffening the same longitudinally, and stiff horizontal beams on said connectors extending to the sides of said thrust-bearing portion and connected thereto and braced to transmit expansion forces of said connectors to said portion, the cylinder-engaging surface of said skirt having a slightly elliptical eccentrlcity with its minor axis substantially parallel to the wristpin axis.

2. An all-aluminum piston having a head. wrist-pin boss connectors depending therefrom and rigidly connected thereto, a skirt having a continuous, thin, flexible cylinder-bearing wall in the region between said connectors and separated from said head, and vertically wide cross beams on said connectors extending horizontally to said wall athwart the wrist-pin axis, said beams being provided with reenforoing means distributed substantially throughout their vertical width to render them substantially unyielding under horizontal loading applied at their ends and oonnected with the lateral portions of said wall with the width of each beam-end extending along a side edge of said wall, the bearing surface of said wall being formed with a slightly elliptical eccentricity.

3. An all-aluminum piston having a head, wrist-pin boss coonnectors depending therefrom and rigidly connected thereto, a skirt having a continuous, thin, flexible cylinder-bearing wall in the region between said connectors and separated from said head, and vertically wide cross beams on said coonnectors extending horizontally to said wall athwart the wrist-pin axis, said beams being provided with reenforcing means distributed substantially throughout their vertical width to render them substantially unyielding under horizontal loading applied at theirv ends and connected with the lateral portions of f said wall with the Width of each beam-end extending along a side edge, the bearing surface of said wall being formed with a slightly elliptical eccentricity, and said wall being thinner at its upper end than at its lower end rendering the same more flexible at its hotter portion.

4. An all-aluminum piston having a head, connectors depending rom said head, a skirt separated from said h ad in the region of one of its bearing faces and having said separated portion continuous and ilexible throughout said region and its bearing face formed with a slightly elliptical eccentricity, webs joined with said'coonnector, provided with bosses and connected at their ends with said skirt portion, and a plurality of transverse ribs spaced vertically along each of said webs extending and increasing in depth from said skirt to said boss.

JOHN FLAIVHVIANG. PERCY L. BOWSER. WILLIAM M. VENNER. PERCY L. BOWSER, JR. 

